1. MANHOLES :

• A manhole, also known as an inspection chamber, provides access to underground utilities, most commonly sewer systems. This enables operatives to undertake inspections, make modifications, and carry out cleaning and maintenance.

• Manholes are generally constructed where there is a change of direction and/or a change in gradient of the utilities, or where access is required for a specific maintenance purpose. They are typically positioned 0.5 m away from curb lines, preferably with the manhole cover positioned away from the wheel line of traffic.

• The cover acts as a plug to protect the manhole and prevent unauthorized access. Covers can be circular, rectangular or square, and are typically made from metal or, less commonly, precast concrete, glass reinforced plastic, or a composite material.

TYPES :

I. Shallow manhole: (0.7 to 0.9m in depth)

II. Normal/medium manhole: (1.5m depth)

III. Deep manhole: (>1.5m depth)

2. Inverted Siphons:

• An inverted siphon or depressed sewer is a sewer that runs full under gravity flow at a pressure above atmosphere in the sewer. Inverted siphons are used to pass under obstacles such as buried pipes, subways, etc. This terminology ‘siphon’ is misnomer as there is no siphon action in the depressed sewer. As the inverted siphon requires considerable attention for maintenance, it should be used only where other means of passing an obstacle in line of the sewer are impracticable.